Removal of organic coatings from substrates is extremely important in many industries. In particular, organic coatings or residues need to be removed from substrates either for the re-working of a part which has a flawed coating or for reclaiming parts in which the substrate is intact but which requires residues to be removed and/or new coatings to be applied.
From U.S. Pat. No. 3,790,489 A, a paint stripping compound is known which is described to be used at elevated temperatures which has a caustic base of an alkali metal hydroxide, an alkali metal nitrate, an alkali metal chloride, a catalyst selected from the group of alkali metal permanganates, manganese dioxide and Cr2O3, and preferably an alkali metal carbonate. The components are fused and maintained at a temperature between 800° F. (about 426° C.) and 900° F. (about 482° C.) for stripping.
However, certain metals, such as zinc, aluminum and magnesium or metallic coatings comprised of metals or alloys thereof, as well as other metals, alloys, and even non-metallic substrates, are subject to chemical attack or destruction under such conditions as taught in U.S. Pat. No. 3,790,489 A. Thus, such caustic compositions are typically avoided in prior art teachings when removing coatings from metals, such as from aluminum, magnesium and zinc.
One prior art approach which is based on high boiling point glycol in a stripping composition is taught by U.S. Pat. No. 6,855,210 B1 and U.S. Pat. No. 7,151,080 B2, wherein stripping from the substrate is achieved by using a composition comprising from about 40% by weight to about 98.9% by weight of a high-boiling alcohol, from about 1% by weight to about 60% by weight of a non-ionic surfactant, and from about 0.1% by weight to about 10% by weight of an alkali hydroxide or mixture of alkali hydroxide, wherein said composition is anhydrous and essentially free of any amines. This method however, requires relatively high operating temperature range (operating temperature is reported to be between 225° F. (about 107° C.) and 350° F. (about 176° C.), more preferably between 250° F. (about 121° C.) and 325° F. (about 162° C.)), thus consuming much energy and also creating some safety concerns. Therefore, it requires an adequate set-up of the processing line for operator's safety. Moreover, as it requires relatively high operating temperature, it has limited use to strip/remove organic coatings from plastic substrates.
As prior art methods (especially U.S. Pat. No. 6,855,210 B1, U.S. Pat. No. 7,151,080 B2) make use of nonylphenol ethoxylate which has proved to be hazardous, WO 2013/117757 A1 teaches another non-aqueous stripping composition which comprises a source of hydroxide ions, a high-boiling alcohol having a boiling point of at least 150° C. and at least one surfactant represented by chemical formula R—O—(CH2CH2O)nH, wherein R is an alkyl chain, linear or branched having a 2 to 30 carbon atom chain length. Operating temperature is reported to be between 100° C. and 200° C. The composition is preferably amine free in order to avoid attack of the substrate material, which would particularly occur on galvanized substrate material.
EP 1 319 694 A1 discloses an agent and a process for stripping lacquer from metal surfaces, particularly from metal surfaces made of non-ferrous metals such as aluminum or aluminum alloys. The main component of the organic paint stripper is an alcoholic organic solvent. A particularly good paint stripping effect is achieved due to the fact that the paint stripper contains, as an additional component, alkoxylated alkyl alcohols.